Methods and Apparatus for Depositing Material Using a Dynamic Pressure

ABSTRACT

A method of depositing organic material is provided. A carrier gas carrying organic material is ejected from a nozzle at a flow velocity that is at least 10% of the thermal velocity of the carrier gas, such that the organic material is deposited onto a substrate. In some embodiments, the dynamic pressure in a region between the nozzle and the substrate surrounding the carrier gas is at least 1 Torr, and more preferably 10 Torr, during the ejection. In some embodiments, a guard flow is provided around the carrier gas.

CROSS-REFERENCES TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 12/823,323, filed Jun. 25, 2010, which is acontinuation-in-part of U.S. application Ser. No. 12/786,982, filed May25, 2010 (now U.S. Pat. No. 7,897,210, issued Mar. 1, 2011), whichclaims priority to U.S. patent application Ser. No. 12/175,641, filedJul. 18, 2008 (now U.S. Pat. No. 7,722,927, issued May 25, 2010), whichis a divisional of U.S. application Ser. No. 10/422,269, filed Apr. 23,2003 (now U.S. Pat. No. 7,404,862, issued Jul. 29, 2008), which is acontinuation-in-part of U.S. application Ser. No. 10/233,470, filed Sep.4, 2002 (now U.S. Pat. No. 7,431,968, issued Oct. 7, 2008), which claimsthe benefit under 35 U.S.C. §119(e) of U.S. Provisional ApplicationsNos. 60/317,215, filed on Sep. 4, 2001, 60/316,264, filed on Sep. 4,2001, 60/316,968, filed on Sep. 5, 2001, and 60/332,090, filed on Nov.21, 2001, and which is related to U.S. application Ser. No. 10/233,482,filed on Sep. 4, 2002 (now U.S. Pat. No. 6,716,656, issued Apr. 6,2004). All of these above-mentioned Applications are herein incorporatedby reference in their entireties. This patent application is also acontinuation-in-part of U.S. application Ser. No. 10/690,704, filed Oct.23, 2003 (now U.S. Pat. No. 7,744,957, issued Jun. 29, 2010), which isincorporated by reference in its entirety.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract No.F49620-92-J-0424 awarded by the U.S. Air Force OSR (Office of ScientificResearch) and Contract No. DAAD 19-02-2-00198 awarded by the ArmyResearch Lab. The government has certain rights in this invention.

RESEARCH AGREEMENTS

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a jointuniversity-corporation research agreement: Princeton University, TheUniversity of Southern California, and Universal Display Corporation.The agreement was in effect on and before the date the claimed inventionwas made, and the claimed invention was made as a result of activitiesundertaken within the scope of the agreement.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method and apparatus for depositingmaterial.

Molecular organic compounds are employed as active materials in avariety of applications, including organic light emitting diodes(OLEDs), organic phototransistors, organic photovoltaic cells, organicphotodetectors, and thin films. Many of the materials used to make suchdevices are relatively inexpensive, so organic opto-electronic deviceshave the potential for cost advantages over inorganic devices. Inaddition, the inherent properties of organic materials, such as theirflexibility, may make them well suited for particular applications suchas fabrication on a flexible substrate. For OLEDs, the organic materialsmay have performance advantages over conventional materials. Forexample, the wavelength at which an organic emissive layer emits lightmay generally be readily tuned with appropriate dopants.

Organic optoelectronic devices such as thin film transistors (TFTs),light emitting diodes (LEDs) and photovoltaic (PV) cells, have gainedconsiderable attention of researchers during the past decade. Organicsemiconductors can be deposited on a variety of substrates, whichpotentially simplifies and lowers fabrication costs when compared toinorganic semiconductors. However, the unique processing requirements oforganic semiconductors can also limit their application. For example,light emitting devices and PV cells typically consist of thin (<100 nm)films of either conjugated polymers or monomers, sandwiched betweenconducting electrodes. For full-color displays and multi-transistorcircuits, the active organic layers themselves must also be laterallypatterned. However, the organic layers are typically too fragile towithstand conventional semiconductor processing methods such asphotolithography, plasma processing, or reactive ion etching. Manyfabrication and patterning techniques have therefore been developed toaddress these unique requirements, emphasizing primarily the ease andlow cost of processing. Recent successes in fabricating OLEDs havedriven the development of OLED displays (see S. R. Forrest, Chem. Rev.97, 1793 (1997)). OLEDs make use of thin organic films that emit lightwhen voltage is applied across the device. OLEDs are becoming anincreasingly popular technology for applications such as flat paneldisplays, illumination, and backlighting. OLED configurations includedouble heterostructure, single heterostructure, and single layer, and awide variety of organic materials may be used to fabricate OLEDs.Several OLED materials and configurations are described in U.S. Pat. No.5,707,745, which is incorporated herein by reference in its entirety.

Typically, these thin (−100 nm) film devices (including OLEDs andphotovoltaic cells) are grown by thermal evaporation in high vacuum,permitting the high degree of purity and structural control needed forreliable and efficient operation (see S. R. Forrest, Chem. Rev. 97, 1793(1997)). However, control of film thickness uniformity and dopantconcentrations over large areas needed for manufactured products can bedifficult when using vacuum evaporation (see S. Wolf and R. N. Tauber,Silicon Processing for the VLSI Era (Lattice, 1986)). In addition, aconsiderable fraction of the evaporant coats the cold walls of thedeposition chamber. Over time, inefficient use of materials results in athick coating which can flake off, leading to particulate contaminationof the system and substrate. The potential throughput for vacuumevaporated organic thin film devices is low, resulting in highproduction costs. Low-pressure organic vapor phase deposition (LP-OVPD)has been demonstrated recently as a superior alternative technique tovacuum thermal evaporation (VTE), in that OVPD improves control overdopant concentration of the deposited film, and is adaptable to rapid,particle-free, uniform deposition of organics on large-area substrates(see M. A. Baldo, M. Deutsch, P. E. Burrows, H. Gossenberger, M.Gerstenberg, V. S. Ban, and S. R. Forrest, Adv. Mater. 10, 1505 (1998)).

Organic vapor phase deposition (OVPD) is inherently different from thewidely used vacuum thermal evaporation (VTE), in that it uses a carriergas to transport organic vapors into a deposition chamber, where themolecules diffuse across a boundary layer and physisorb on thesubstrate. This method of film deposition is most similar to hydridevapor phase epitaxy used in the growth of III-V semiconductors (see G.B. Stringfellow, Organometallic Vapor-Phase Epitaxy (Academic, London,1989); G. H. Olsen, in GaInAsP, edited by T. P. Pearsall (Wiley, NewYork, 1982)). In LP-OVPD, the organic compound is thermally evaporatedand then transported through a hot-walled gas carrier tube into adeposition chamber by an inert carrier gas toward a cooled substratewhere condensation occurs. Flow patterns may be engineered to achieve asubstrate-selective, uniform distribution of organic vapors, resultingin a very uniform coating thickness and minimized materials waste.

Using atmospheric pressure OVPD, Burrows et al. (see P. E. Burrows, S.R. Forrest, L. S. Sapochak, J. Schwartz, P. Fenter, T. Buma, V. S. Ban,and J. L. Forrest, J. Cryst. Growth 156, 91 (1995)) first synthesized anonlinear optical organic salt 4′-dimethylamino-N-methyl-4-stilbazoliumtosylate. In a variation on this method, Vaeth and Jensen (see K. M.Vaeth and K. Jensen, Appl. Phys. Lett. 71, 2091 (1997)) used nitrogen totransport vapors of an aromatic precursor, which was polymerized on thesubstrate to yield films of poly (s-phenylene vinylene), alight-emitting polymer. Recently, Baldo and co-workers (see M. A. Baldo,V. G. Kozlov, P. E. Burrows, S. R. Forrest, V. S. Ban, B. Koene, and M.E. Thompson, Appl. Phys. Lett. 71, 3033 (1997)) have demonstrated whatis believed to be the first LP-OVPD growth of a heterostructure OLEDconsisting of N,N-di-(3-methylphenyl)-N,N diphenyl-4,4-diaminobiphenyland aluminum tris(8-hydroxyqumoline) (Alq₃), as well as an opticallypumped organic laser consisting of rhodamine 6G doped into Alq₃. Morerecently, Shtein et al. have determined the physical mechanismscontrolling the growth of amorphous organic thin films by the process ofLP-OVPD (see M. Shtein, H. F. Gossenberger, J. B. Benziger, and S. R.Forrest, J. Appl. Phys. 89:2, 1470 (2001)).

Virtually all of the organic materials used in thin film devices havesufficiently high vapor pressures to be evaporated at temperatures below400° C. and then to be transported in the vapor phase by a carrier gassuch as argon or nitrogen. This allows for positioning of evaporationsources outside of the reactor tube (as in the case of metalorganicchemical vapor deposition (see S. Wolf and R. N. Tauber, SiliconProcessing for the VLSI Era (Lattice, 1986); G. B. Stringfellow,Organometallic Vapor-Phase Epitaxy (Academic, London, 1989))), spatiallyseparating the functions of evaporation and transport, thus leading toprecise control over the deposition process.

Though these examples demonstrate that OVPD has certain advantages overVTE in the deposition of organic films, especially over large substrateareas, the prior art has not addressed the special problems that arisewhen depositing an array of organic material.

As is the case for fabrication of arrays using VTE, to adapt OVPD toOLED technology, a shadow mask delineating the shape of the desiredpixel grid is placed close to the substrate to define the pattern ofdeposition on the substrate. Control of the shadow mask patterning is acritical step, for example, in the fabrication of full-color OLED-baseddisplays (see U.S. Pat. No. 6,048,630, Burrows, et al.). Ideally, theresultant pattern on a substrate is identical to that cut into theshadow mask, with minimal lateral dispersion and optimal thicknessuniformity of the deposited material. However, despite the overalladvantages of OVPD in depositing organic layers, the use of the shadowmask in OVPD has certain disadvantages including: significant lateraldispersion compared to VTE; material waste; potential for dustcontamination on the film from the mask; and difficulty in controllingthe mask-substrate separation for large area applications.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be an fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

Early methods of patterning organic materials involved the deposition oforganic materials through a mask. The organic materials may be depositedthrough an “integrated” mask which is attached to the substrate on whichthe device is being fabricated, as disclosed in U.S. Pat. No. 6,596,443,issued on Jul. 22, 2003, which is incorporated by reference in itsentirety. Or, the organic materials may be deposited through a shadowmask that is not integrally connected to the substrate, as disclosed inU.S. Pat. No. 6,214,631, issued on Apr. 10, 2001, which is incorporatedby reference in its entirety. However, the resolution that may beachieved with such masks is limited due to a number of factors,including the resolution to which a mask may be reliably fabricated, thebuildup of organic material on the mask, and the diffusion of organicmaterial in between the mask and the substrate over which it is beingdeposited.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. For example, for a devicehaving two electrodes, the bottom electrode is the electrode closest tothe substrate, and is generally the first electrode fabricated. Thebottom electrode has two surfaces, a bottom surface closest to thesubstrate, and a top surface further away from the substrate. Where afirst layer is described as “disposed over” a second layer, the firstlayer is disposed further away from substrate. There may be other layersbetween the first and second layer, unless it is specified that thefirst layer is “in physical contact with” the second layer. For example,a cathode may be described as “disposed over” an anode, even thoughthere are various organic layers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

“Ambient” as used herein refers to the default state of a parameter,when no effort is made to control that parameter beyond the normalefforts associated with a home or office building. For example, ambientatmosphere is 1 atm (or thereabout depending on elevation) having thegeneral chemical composition of air, and ambient temperature is roomtemperature, or approximately 25 degrees C. (or thereabout).“Background” pressure is the pressure in a chamber (vacuum orotherwise), measured far from any effects caused, for example, by anOVJP jet.

BRIEF SUMMARY OF THE INVENTION

The present invention may provide methods for the patterned depositionof organic materials onto substrates without the need for a shadow mask.

A method of depositing organic material is provided. A carrier gascarrying an organic material is ejected from a nozzle at a flow velocitythat is at least 10% of the thermal velocity of the carrier gas, suchthat the organic material is deposited onto a substrate.

In some embodiments, the dynamic pressure in a region between the nozzleand the substrate surrounding the carrier gas is at least 1 Torr, andmore preferably 10 Torr, during the ejection. In some embodiments, aguard flow is provided around the carrier gas. In some embodiments, thebackground pressure is at least about 10e-3 Torr, more preferably about0.1 Torr, more preferably about 1 Torr, more preferably about 10 Torr,more preferably about 100 Torr, and most preferably about 760 Torr.

A device is also provided. The device includes a nozzle, which furtherincludes a nozzle tube having a first exhaust aperture and a first gasinlet; and a jacket surrounding the nozzle tube, the jacket having asecond exhaust aperture and a second gas inlet. The second exhaustaperture completely surrounds the first tube aperture. A carrier gassource and an organic source vessel may be connected to the first gasinlet. A guard flow gas source may be connected to the second gas inlet.The device may include an array of such nozzles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of an OVJP apparatus having multiple sourcecells.

FIG. 2 shows an embodiment of an OVJP nozzle that can produce a guardflow.

FIG. 3 shows a schematic of an OVJP nozzle illustrating carrier gas andorganic molecule trajectories.

FIG. 4 shows a plot of the qualitative dependence of the normalizeddeposit width vs. downstream pressure, and a related plot of thequalitative relationship between nozzle radius, nozzle/substrateseparation, and downstream pressure.

FIG. 5 shows calculated velocity and flow lines for particles ejectedfrom a nozzle.

FIG. 6 shows calculated thickness profiles for various downstreampressures.

FIG. 7 shows calculated thickness profiles for various nozzle—substrateseparation distances.

FIG. 8 shows an image printed by OVJP.

FIG. 9 shows an optical micrograph of pentacene dots printed by OVJP.

FIG. 10 shows an optical micrograph of Alq₃ dots printed by OVJP.

FIG. 11 shows thickness profiles for the dots of FIG. 7.

FIG. 12 shows a plot of the full width half maximum of the thicknessprofiles of FIG. 9 v. the square root of nozzle-substrate separation.

FIG. 13 shows a scanning electron micrograph of a pentacene linedeposited by OVJP.

FIG. 14 shows a plot of drain-source current v. drain-source voltage fora TFT deposited by OVJP.

FIG. 15 shows a plot of drain-source current v. gate-source bias for aTFT deposited by OVJP.

FIG. 16 shows an embodiment of an OVJP apparatus.

FIG. 17 shows an enlarged cross-sectional view of a source cell shown inFIG. 6.

FIG. 18 shows an enlarged side view of a source cell shown in FIG. 16.

FIG. 19 shows another embodiment of an OVJP apparatus.

FIG. 20 shows a further embodiment of an OVJP apparatus.

FIG. 21 shows a photograph of the deposited organic material fromExample 1 showing interference fringes due to the variation in thicknessof the deposited organic material.

FIG. 22 shows a photograph of the deposited organic material fromExample 2 showing interference fringes due to the variation in thicknessof the deposited organic material.

FIG. 23 shows the light intensity profile of the photograph of thedeposited organic material from Example 2, and the physical shape of thedeposited organic material from Example 2.

FIG. 24 shows the structure of an OLED fabricated in-part by anembodiment of the device of the invention.

FIG. 25 shows a plot of the electroluminescent (EL) intensity as afunction of wavelength for the OLED fabricated in Example 3.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described with reference to the followingillustrative embodiments.

As described in U.S. application Ser. No. 10/233,470, filed Sep. 4, 2002(now U.S. Pat. No. 7,431,968), which is incorporated herein by referencein its entirety, organic vapor jet deposition (OVJD) is a technique thatallows for direct patterning of organic films on substrates. In general,OVJD also may be referred to herein as organic vapor jet printing(OVJP). OVJD, or OVJP, uses an inert carrier gas, such as nitrogen orargon, to transport the organic vapors from their source(s) and ejectthem from one or more nozzles, producing collimated jets of organicvapor and carrier gas. Upon striking the substrate, the organic vaporsare condensed out of the jet, forming a patterned deposit, whose shapecan be controlled by engineering the nozzle shape and flow dynamics ofthe organic vapor and carrier gas.

Organic vapor jet printing (OVJP) allows for the direct patterningduring growth of molecular organic semiconductor thin films. A hot inertcarrier gas picks up organic vapor and expands through a microscopicnozzle, resulting in a highly collimated jet. The jet impinges on a coldsubstrate, leading to the selective physisorption of the organicmolecules but not the carrier gas. The non-equilibrium nature of OVJPallows for high resolution, nearly 100% efficient, direct printing oforganic semiconductor patterns and devices. The deposition rates may bevery high, for example up to and exceeding 1000 Å/s. We demonstratepattern resolution determined in part by the nozzle diameter andseparation from the substrate. For example, employing a 20 μm diameterorifice, we obtained patterns of ˜25 μm in diameter (1000 dots perinch). Further, we print an archetypal pentacene channel thin filmtransistor at a film deposition rate of 700 Å/s, resulting in holemobility of 0.25 cm²/V·s and current on/off ratio of 7·10⁵, (comparableto performance achieved with vacuum deposited devices). Using a scalinganalysis the influence of process conditions on the printing resolutionand speed are determined. Combinatorial printing experiments and directsimulation Monte-Carlo models support the analysis. The printing ofmolecular organic semiconductors by OVJP allows for the rapidfabrication of both small- and large-scale electronic circuits. Theprocess can be carried out in a range of upstream-to-downstream pressuregradients, depending on the nozzle size and number, while the downstreampressure preferably ranges from 0.1 to 1000 Torr. Due to the highlylocalized and directional characteristic of OVJP, embodiments of theinvention allow for the direct organic film patterning is possible forsubstrates of virtually arbitrary size and shape. In addition to organicelectronic device application, the method of OVJP provides access to newfilm growth regimes using highly localized hyperthermal organic beams,with additional, new degrees of control of film and crystal morphology.

In embodiments of organic vapor jet printing (OVJP), a hot inert carriergas picks up molecular organic vapor and expands through a microscopicnozzle. The resulting collimated gas jet impinges onto a cold substrate,leading to the selective, localized deposition of the organic molecules,but not the carrier gas. Because OVJP does not use liquid solvents, itallows for greater latitude in the choice of substrate material andshape than other processes such as ink-jet printing, thereby permittinga wider variety of organic semiconductors and structures to bedeposited. The molecules used for organic devices are typically stableagainst decomposition and pyrolysis up to 350-450° C., while havingvapor pressures of up to several millibar, allowing high practicaldeposition rates.

One unique aspect of OVJP is that the organic species can be acceleratedby the flow of a much lighter carrier gas to hyperthermal velocities.This can lead to denser and more ordered thin films, which potentiallybroadens the processing window for ultra-rapid growth of high qualitythin films for device applications. This acceleration may also theinstantaneous local deposition rate of OVJP to exceed that of thealternative broad-area deposition methods, resulting in a competitiveadvantage in the rapid printing of large-scale electronics. A typicalOLED heterostructure is 2000 Å thick. At 1000 Å/s and using a lineararray of nozzles, each having a diameter to match the pixel width, a1000 pixel wide display can be printed in ˜30 minutes. The growth ratesin the experiments discussed herein are already several orders ofmagnitude higher than the typical rates reported for fabrication ofmolecular organic electronic devices, but they can be increasedfurther—for each 10° C. increase in the source temperature, theevaporation rate approximately doubles. OVJP is preferably used todeposit small molecule organic materials because they generally havesufficient vapor pressure at reasonable temperatures to allow for a highdeposition rate. However, OVJP may have applications to other materials,such as polymers.

Embodiments of OVJP generally involve a “jet” of gas ejected from anozzle, as distinct from other techniques, such as OVPD (organic vaporphase deposition), where a carrier gas may be used, but there is no“jet.” A “jet” occurs when the flow velocity through the nozzle issufficiently large to result in a significantly anisotropic velocitydistribution relative to the isotropic velocities of a stagnant gas withmolecules bouncing around. One way of defining when a jet occurs is whenthe flow velocity of the carrier gas is at least 10% of the thermalvelocity of the carrier gas molecules.

More generally, embodiments of the invention allow for patterned vaporphase deposition at pressures higher than previously thought possible ina region between a nozzle and a substrate. Specifically, this “regionbetween a nozzle and a substrate” is the region surrounding the jet ofcarrier gas as it travels from the nozzle to the substrate, which mayinteract with the jet. One way of controlling the pressure in thisregion is through the background pressure, which is the pressure in theroom, vacuum chamber, or other area in which the deposition isoccurring—for example, by depositing in a vacuum chamber. Another way ofcontrolling this pressure is though the use of a guard flow, asdescribed herein and as illustrated in FIG. 2, for example. A guard flowmay be desirable even in a pressure controlled environment such as avacuum chamber, to mitigate the effect of any impurities that may bepresent.

An embodiment of an OVJP apparatus is schematically illustrated inFIG. 1. Device 100 includes a first organic source cell 110, a secondorganic source cell 120, a dilution channel 130, a mixing chamber 140, anozzle 150, and heating elements 160. Organic source cells 110 and 120may contain organic materials for deposition on a substrate 170. Eachorganic source cell may contain a different organic material orcombination of organic materials. Carrier gas source(s) 105,schematically represented as arrows, may provide a flow of carrier gasto organic source cells 110 and 120, and dilution channel 130. Valves orother mechanisms may be used to determine whether, and how much, carriergas flows through each of the organic source cells 110 and 120, anddilution channel 130. When a carrier gas flows through an organic sourcecell, the organic material contained therein may sublimate, and issubsequently carried by the carrier gas. The organic material andcarrier gas then mixes in the mixing chamber with any other carrier gasand/or organic materials that enters from either the dilution channel oranother organic source cell. Dilution channel 130 may be used to achievemore precise control at lower organic material concentrations than mightbe possible without a dilution channel. The mixture of one or moreorganic materials and carrier gas is then expelled through nozzle 150towards substrate 170. Heating elements 160 may be used to control thetemperature of the carrier gas and organic materials in device 100. Bycontrolling the flow velocity and other parameters as explained herein,the flow mechanics of the expelled material may be controlled to form acollimated jet 155. Substrate 170 is disposed over a substrate holder180, which may include a cooling channel 190. Any suitable positioningmechanism may be used to control the relative positions of substrate 170and device 100. Cooling channel 190 may be connected to a coolantsource, and may be used to control the temperature of substrate holder180 and substrate 170. The organic material is then deposited onsubstrate 170, and the carrier gas flows away to the sides.

Device 100 may be made of any suitable material. Stainless steel ispreferred for its durability and heat conductivity. Although only twoorganic source cells 110 and 120 are shown for clarity, more or lessorganic source cells may be used. Preferably, heating elements 160 mayachieve a uniform heating of device 100. Preferably, individuallymetered carrier gas streams flow through each source cell to regulatethe rate of delivery of the organic vapor. Device 100 also allows for“make-up” and “pusher” gas flow through dilution channel 130. A make-upgas flow may be used to regulate the concentration of organic vapor inaddition to the source temperature. Pusher gas flow helps to avoidback-diffusion of vapor. In the embodiment of FIG. 1, both make-up andpusher functions may be achieved through dilution channel 130. Themotion of substrate 170 is preferably along all 3 axes andcomputer-controlled.

Another embodiment of an OVJP apparatus is schematically illustrated inFIG. 2. Nozzle 200 comprises a nozzle tube 210 and a jacket 220. Nozzletube 210 is defined by nozzle tube wall 217. Jacket 220, which isdisposed adjacent to nozzle 210, is defined by nozzle tube wall 217 andjacket wall 227. Nozzle tube 210 has a first gas inlet 212 and a firstexhaust aperture 215. Jacket 220 has a second gas inlet 222 and a secondexhaust aperture 225. A carrier gas source 230 provides a flow ofcarrier gas carrying organic material to first gas inlet 212. A guardflow source 240 provides a flow of guard flow gas to second gas inlet222. The carrier gas, carrying material to be deposited, flows out offirst exhaust aperture 215. The guard flow gas flows out of secondexhaust aperture 225. The gas sources of FIG. 2 are illustratedgenerally, and may include any components associated with providing acontrolled gas flow to the nozzle, such as tubes, valves, gas cylinders,temperature control apparati, and other components.

In heated embodiments, heat may be provided in a variety of ways. Thecarrier gas source is preferably heated to a temperature suitable tosublimate, in a source cell, the appropriate concentration of moleculeto be deposited. Other heat sources may be desirable to prevent themolecule from depositing onto the nozzle and elsewhere (other than thesubstrate, where deposition is desired) as it progresses out of thesource cell and beyond. Preferably, the guard flow source providesheated guard flow gas, which then heats nozzle tube wall 217. Otherheated embodiments may be achieved by using RF or other heatingmechanisms to directly heat parts of nozzle 200, such as nozzle tubewall 217 and/or jacket wall 227.

An appropriate guard flow may confine the carrier gas and the moleculesbeing deposited, and prevent them from spreading. Thus, a desirablesharper and higher resolution may be achieved. Preferably, the guardflow comprises a relatively heavy gas as compared to the carrier gas.Preferably, the guard flow gas is heavier than the molecular weight ofthe carrier gas, which enables the guard flow to more effectivelycontain the carrier gas.

Although the deposition can be carried out at atmospheric conditions,the downstream pressure, P_(L)., is reduced to 0.1-10 Torr in someembodiments to promote mass transport. To maintain the edge sharpnessfor deposited patterns as small as 25 μm the nozzle-to-substrateseparation, s, is kept on the order of the molecular mean free path, λ,at the deposition pressure, (e.g. 100 um>λ>1 μm for 0.1 Torr<P_(L), <10Torr). Edge sharpness is preferred for some embodiments but notnecessary. When λ, is on the order of the apparatus dimension (which canbe taken as either s, the nozzle diameter, a, or nozzle length, L), theflow is said to undergo a transition from the continuum to the freemolecular flow regimes. Typical OVJP conditions result in suchtransition regime flow.

A description of the physical picture of transitional flow may bederived from experiment and direct simulation Monte-Carlo (DSMC)techniques. The present specification, in addition to demonstrating OVJPof high-resolution organic thin film patterns and devices, examines howprocess conditions affect the growth rate and pattern resolution. Ascaling model is developed and compared to DSMC simulations and OVJPexperiment.

A mass balance on the organic species in the source cell (7) gives theexpression for the vapor pressure of the organic species exiting thesource cell:

$\begin{matrix}{P_{org} = \frac{P_{org}^{sat} \cdot k}{k + {\overset{.}{V}/{RT}_{cell}}}} & (1)\end{matrix}$

where P_(org) is the vapor pressure, P_(org) ^(sat) is the saturation(equilibrium) vapor pressure of the organic material, {dot over (V)} isthe carrier gas volumetric flow velocity, and k is a constant describingthe kinetics of the evaporation from the organic surface inside thesource cell. Equation (1) shows that the carrier gas flow rate, as wellas the source temperature, may regulate the flux of organic vapor, whichis a consideration for regulating the concentration of dopants in thedeposited films.

Downstream from the source cell, OVJP differs significantly fromvapor-phase deposition and ink jet printing. Unlike vapor-phasedeposition, OVJP is not diffusion limited near the substrate, and,unlike ink jet printing, OVJP does not take place in the liquid phase.The flow rate of gas through the nozzle, Q, is the product of thepressure driving force and the nozzle conductance:

Q=C·(P _(H) −P _(L))  (2)

where the driving force is the difference in the upstream and downstreampressures (P_(H) and P_(L)), and the conductance, C, is expressed as:

$\begin{matrix}{C = {\left\lbrack {\frac{4}{3L}\sqrt{\frac{2\pi \; {kT}}{M}a^{3}}} \right\rbrack \cdot \left( {{0.1472\; \frac{a}{\lambda}} + \frac{1 + {3.50{a/\lambda}}}{1 + {5.17{a/\lambda}}}} \right)}} & (3)\end{matrix}$

where the quantity in the first brackets is calculated from the kinetictheory, and then modified by an empirical factor for different gasmixtures and conditions. Due to the large difference in the molecularweights of the organic and carrier gas species used in OVJP, Eq. (3) maybe further corrected to reflect thermal slip near the inner wall of thenozzle.

While the light carrier gas species are strongly scattered radially bythe substrate, the heavier organic species retain more of their axialmomentum (in proportion to the ratio of the organic molecular masse tothat of the carrier gas, m_(o)m_(c)). This mechanism is confirmed byDSMC results, as shown in FIGS. 4 and 5. If the separation s is on theorder of the 2 near the substrate, the organic molecules suffer fewcollisions within the nozzle-substrate gap. Assuming that the organicmoieties attain the bulk flow velocity ū inside the nozzle, theirtransport rate u_(z) in the z-direction is:

u _(z) ≈ū=Q/πα ²  (5)

The average velocity with which the organic molecules are dispersedradially outward from the nozzle may be expressed as:

$\begin{matrix}{u_{r} \approx {{\overset{\_}{u} \cdot \frac{a}{2s} \cdot \frac{m_{c}}{m_{o}} \cdot \frac{s}{\lambda}} + v_{D}}} & (6)\end{matrix}$

where χ is the radial distance traveled after emerging from the nozzle,m_(c) and m_(o) are the carrier gas and organic molecular weights,respectively, while V_(D), is the contribution from pure diffusivity ofthe organic particle. This (isotropic) diffusion contribution can beapproximated by:

$\begin{matrix}{v_{D} = \frac{\sqrt{6{Dt}}}{t}} & (7)\end{matrix}$

where D and t are the gas diffusivity of the organic species and thetime spent en route to the substrate, respectively.

Assuming fully developed flow inside the nozzle, a low (<1% molar)concentration of the organic species, incompressible flow and massconservation of the carrier gas phase, it can be shown that the organicmolecules travel radially outward from their original position in thenozzle by a distance χ:

$\begin{matrix}{\frac{\chi}{a} = {{\frac{m_{c}}{m_{o}} \cdot \frac{s}{\lambda}} + \sqrt{\frac{1}{3} \cdot \frac{\overset{\_}{c} \cdot s \cdot \lambda}{\overset{\_}{u} \cdot a^{2}}}}} & (8)\end{matrix}$

where, m_(c)/m_(o) is the organic-to-carrier gas molecular mass ratio, cis the molecular mean thermal velocity, and ū is the mean flow velocityinside the nozzle. The first term in Eq. (8) quantifies the horizontalmomentum transfer to the organic molecules from collisions with thediverging carrier gas, while the second term represents the scaling ofthe radial diffusion rate to the ballistic transport rate normal to thesubstrate.

Although Eq. (8) does not predict the exact deposit shape, it shows therelative influence of process conditions on the deposited patternresolution. In particular, given that λ=kT/√{square root over(2σP_(L))}, where σ is the cross-section of the molecule, the dispersionhas a minimum for some value of P_(L), as shown in FIG. 3. The value ofP_(L) corresponding to maximum resolution is in the range of 1-50 Torrfor typical OVJP conditions. Equation (8) also suggests that patterndefinition is enhanced through use of a lighter carrier gas (e.g. Heinstead of N₂). Practically, ū is fixed by the desired deposition ratevia the total flux of the organic molecules in the nozzle. Thus, for agiven nozzle radius a, the remaining adjustable parameters are s andP_(L). The operating conditions for maximum pattern resolution can thusbe plotted on a process diagram (FIG. 4), where the operating linedictates values of s for any given P_(L). For example, to maintain highpattern resolution even at large separation, s, the downstream pressure,F_(L), may be decreased. The region above the operating line representsdiffusion-limited printing, while the region below corresponds toconvection-limited operation. Finally, the local dynamic pressure in theregion between the nozzle and the substrate generally exceeds P_(L) andscales inversely with s. This places a lower limit on the effectiveF_(L), as indicated by the “Dynamic Pressure Line”, such that theminimum in the pattern dispersion curve with P_(L) may not be observableunder practical OVJP conditions.

A common feature of a single nozzle expansion is that it produces a fluxprofile domed in the center for virtually all upstream and downstreamconditions. Thus, to achieve a flattened-top deposit, the nozzle can berastered over an area. Alternatively, a bundle of nozzles or aminiaturized “showerhead” can be used to produce the same effect. Sincethe conductance of a nozzle scales with α³ (see Eq.4), the printingspeed can be maximized in the latter approach. Furthermore, in view ofEq. (8), an annular guard flow of a relatively heavy gas (e.g. Ar orSF₆) may be used in conjunction with a main flow of a lighter gas (e.g.H₂ or He) to increase deposit sharpness. The annular guard flow may beused in connection with other methods of increasing sharpness, such asrastering and the showerhead approach. With a guard flow, the organicspecies are maximally accelerated and collimated by the main carrier gasflow, while the radial diffusion of species is hindered by the guardflow made up of a heavier inert gas.

FIG. 3 shows a schematic illustrated of a nozzle 300 having a hollowcylindrical configuration, in the vicinity of a substrate 310. Carriergas stream lines (solid black lines) and an expected trajectory of anorganic molecule (curved arrow) are qualitatively illustrated. Severalvariables from Equations 1-8 are illustrated as well. Although thecarrier gas flow field rapidly diverges due to the proximity of thesubstrate to the nozzle outlet, the relatively heavy organic moleculesacquire trajectories substantially more collimated than the carrier gas.As discussed herein, the interplay between diffusive and convectiveprocesses at the nozzle orifice dictates the relationship between thepattern shape, nozzle radius (a), nozzle-to-substrate separation (s),and the pressure in the region downstream from the nozzle (P_(L)). Thescaling is usually such that s, the pattern resolution, and themolecular mean free path (A) at F_(L) are of the same magnitude, asindicated in FIG. 3. This implies that downstream from the nozzle,transport is intermediate between continuum and molecular flow.Experiment and direct simulation Monte-Carlo (DSMC) techniques are thebest ways to obtain an understanding of this type of transport.

FIG. 4 shows a plot of the qualitative dependence of the patterndispersion, χ/α, on the downstream pressure, P_(L), and a related plotof the relationship between nozzle radius, nozzle/substrate separation,and downstream pressure. Plot 410 shows a plot of the qualitativedependence of the pattern dispersion, χ/α, on the downstream pressure,P_(L). The dispersion is minimized at a given value of P_(L), due to theopposing balance of convective and diffusive transport rates. Plot 420shows a plot of the relationship between nozzle radius, nozzle/substrateseparation, and downstream pressure, for the region identified by acircle in plot 410. The conditions for the highest pattern resolution(minimum dispersion) are plotted to give the optimum operating line.Working above or below this line may decrease pattern resolution.Increasing s and P_(L), results in diffusion controlled transport, whiledecreasing s and P_(L) results in convection controlled transport. Theactual “dynamic pressure,” i.e. the pressure between the nozzle and thesubstrate surrounding the jet, may be higher than the ambient (orbackground) pressure P_(L), due to the interaction between the jet andthe ambient pressure. Hence, the “dynamic pressure” line is lower andsets the practical operating regime. The operating regime signified bythe shaded region under the dynamic pressure line is inaccessible bysome embodiments. Without being limited to any theory as to how theinvention works, it is believed that the jet flow decelerates near thesubstrate, and a part of the kinetic energy of the jet stream isconverted into potential energy in the form of a higher pressure in theregion immediately surrounding the jet stream.

While there is no simple qualitative relationship that exactlydetermines the dynamic pressure as a function of various relevantparameters such as the background pressure, the stream velocity, etc.,it is believed that the dynamic pressure will generally not exceed 10times the background pressure for the case of a jet ejected from anozzle without a guard flow, at velocities reasonably contemplated forOVJP, and where the nozzle-substrate separation is on the same order ofmagnitude as the nozzle radius. In most cases, the dynamic pressure willnot exceed twice the ambient pressure. The simulation needed todetermine the dynamic pressure is well within the skill of one in theart based on the disclosure herein.

Details of the flow calculated by DSMC are shown in FIG. 5. Plot 510shows a vertical velocity component of the flow field. The correspondingtrajectories of the carrier gas and the organic molecules (in this case,tris-(8-hydroxyquinoline)-aluminum, or Alq₃) plotted in plot 520. Thevelocity map shows the acceleration of the flow through the nozzle,reaching a velocity ˜200 m/s at the nozzle exit, and the stagnationfront immediately above the substrate surface, where the dynamicpressure generally exceeds the ambient pressure, P_(L), far away fromthe nozzle region. Velocity is represented as shading on plot 510, withthe highest velocity in the nozzle, and the lowest furthest away fromthe nozzle. The heavy organic molecular trajectories, however, cross thecarrier gas flow lines, resulting in a well-defined deposit. Preferably,the molecular weight if the organic material is greater than themolecular weight of the carrier gas to achieve this divergence betweenthe organic trajectories and the carrier gas trajectories.

The deposit profiles obtained from DSMC for different printingconditions are plotted in FIGS. 6 and 7, where the broadening of thedeposit due to increasing s and P_(L) is evident. The pattern widthfirst varies slowly with P_(L), but then increases rapidly, indicatingthat the conditions are near the dispersion minimum, but that thedynamic pressure exceeds P_(L).

It is believed that the profile of the deposited material is favorablyaffected by a dynamic pressure of at least 1 Torr, and more preferablybe a dynamic pressure of at least 10 Torr.

In some embodiments, specific apparatus configurations may be used toachieve specific deposition advantages or arrangements. For example, anembodiment of the device can be used to pattern both single-componentand doped organic thin films on a substrate. Furthermore, embodiments ofthe device of the invention can be used for the rapid deposition oflaterally patterned, doped films and multi-layer structures.

In an embodiment of the device as depicted in FIG. 16, the deviceincludes a nozzle 1, and an apparatus 2, with one or more source cells4, integrally connected to the nozzle 11 via a mixing chamber 3. In thisembodiment, the integral connection between the apparatus 2 and the oneor more nozzles 1 refers to their close, proximal relationship. Althoughthe apparatus 2 and the one or more nozzles 1 are not necessarilyrigidly connected to each other nor made from a single piece ofmaterial, they are situated close enough together such that they can bemoved together as a single unit. The apparatus 2 also includes a carriergas inlet channel 5 leading to each source cell 4, a carrier gas outletchannel 6 leading from each source cell 4 to the mixing chamber 3, and afirst valve 7 capable of controlling the flow of a carrier gas throughthe one or more source cells 4. In addition, the apparatus 2 includes adilution channel 10 located in the middle of the apparatus 2 which canbe used to allow carrier gas to pass through to the mixing chamber 3without passing through a source cell 4, thereby diluting theconcentrations of the organic vapors in the mixing chamber 3. Thedilution channel 1610 can also serve as a pressure relief channel forthe device. In addition, although the dilution channel 1610 is locatedin the middle of the apparatus 2 in the embodiment of the device asdepicted in FIG. 16, other embodiments of the device can include thedilution channel 1610 located at other positions within the apparatus 2.

In a preferred embodiment of the invention, there are a plurality ofsource cells 4 to enable the deposition of multiple organic materialsthrough a single mixing chamber 3 and nozzle 1. The flow of carrier gasthrough the source cells 4 may be separately controlled for each sourcecell 4, such that different organic materials or different mixtures oforganic materials may be deposited at any given time. For example, as isknown in the art of manufacturing OLEDs, the emissive layer of an OLEDmay contain an emissive organic molecule (a dopant) doped into adifferent organic host material. Thus, this preferred embodiment of theinvention could include a source cell 4 containing an organic dopantmaterial, such as fac tris(2-phenylpyridine) iridium (Ir(ppy)₃), andanother source cell 4 containing an organic host material, such as4,4′-N,N′-dicarbazole-biphenyl (CBP), wherein the flow of carrier gasthrough these source cells 4 is controlled such that the desired amountsof CBP and Ir(ppy)₃ are transported into the mixing chamber 3.Thereafter, the resulting organic layer deposited by such an embodimentof the device comprises a CBP layer doped with Ir(ppy)₃.

In the embodiment shown in FIG. 16, the apparatus 2 comprises asingle-piece structure in the form of a cylinder containing one or moresource cells 4 (only one of which is shown in FIG. 16), with each sourcecell containing an organic material. Each of the source cells 4, whichare also in the form of cylinders, are contained in a cylindrical sourcebore 8 in the apparatus. Although both the apparatus 2 and the sourcecells 4 (along with the accompanying cylindrical source bores 8) are inthe form of a cylinder in FIG. 16, the apparatus and the source cellsmay be in various other geometrical forms, including but not limited to,a square block, a rectangular block, a hexagonal block, and an octagonalblock. Furthermore, both the apparatus and the source cells may havetapered geometries, such that the inlet and outlet ends of the apparatusand/or source cell would have different radii or dimensions. Inaddition, although the embodiment of the device shown in FIG. 16includes a single source cell 4 contained in a cylindrical source bore8, additional source cells 4 may be positioned in a linear arrangementin a single cylindrical source bore 8.

In other embodiments of the device of the invention, the apparatus isnot in the form of a single-piece structure, but instead comprises oneor more separate structures, wherein each structure contains one of theone or more source cells. Furthermore, the separate structures could berigidly attached to each other to increase the strength of the apparatusas a whole. The structure could be any type of physical form, such as atube or a hollow square block, capable of containing one or more sourcecells. For example, the apparatus could comprise one or more tubes, witheach tube containing one of the one or more source cells.

In the embodiment shown in FIG. 16, the first valve 7 includes aplurality of source-cell valves, wherein each source-cell valve isassociated with each carrier gas inlet channel 5. That is, eachsource-cell valve corresponds to a source cell 4 such that thesource-cell valve is capable of controlling the flow of the carrier gasinto each carrier gas inlet channel 5. By carefully selecting theopening and closing of selected source-cell valves, the device shown inFIG. 16 can be used for the selective patterned deposition of organicvapors, for example, on a substrate.

In the embodiment of the invention shown in FIG. 16, the source cell 4has a first cylindrical portion having a first radius, while each of thecylindrical source bores 8 has a second radius which is slightly largerthan the first radius of the source cell 4. As used herein, the phrase“slightly larger” means allowing for the rotation of the source cells 4within the cylindrical source bore 8, but impeding the flow of carriergas therethrough. Also shown in FIG. 16 is a valve 7 including anaperture 9 in the source cell 4 that aligns with the inlet channel 5when the source cell 4 is in a first position, and does not align withthe inlet channel 5 when the source cell 4 is in a second position. Bythis arrangement, shown in FIG. 16 and described above, each source cell4 can be turned to an “on” position by rotating the source cell 4 aboutits own longitudinal axis into the first position, wherein the aperture9 does align with the inlet channel 5. In this first position, carriergas can flow through the carrier gas inlet channel 5, the source cell 4,the carrier gas outlet channel 6, the mixing chamber 3 and the nozzle 1.In addition, each source cell 4 can be nearly hermetically sealed in an“off” position by rotating the source cell 4 about its own longitudinalaxis into the second position, wherein the aperture 9 does not alignwith the inlet channel 5, thereby not allowing for the flow of carriergas through the source cell 4.

Preferably, in the embodiment shown in FIG. 16, the source cell 4 with afirst cylindrical portion having a first radius, and each of thecylindrical source bores 8 having a second radius which is slightlylarger than the first radius of the source cell 4, are sized and fittedsuch that hot-valving occurs when using the device. As used herein, theterm “hot-valving” refers to the opening and/or closing of a hot,gas-tight seal between a source cell 4 and a cylindrical source bore 8.The hot (preferably in the range of about 150° to about 500° C., morepreferably about 215° C.), gas-tight seal is preferred to prevent theundesired passage of carrier gas through the apparatus and out of thenozzle, which could generally not he achieved with the use of lubricantsand/or elastomeric seals (such as elastomeric o-rings) which arecommonly used in liquid-based systems, such as ink-jet printing methodsand devices. In addition, known sealants and lubricants for gas-basedsystems, such as teflon and graphite, can be used in accordance with theinvention.

FIG. 17 shows an enlarged version of the embodiment of the source cell 4shown in FIG. 16. The reference numbers in FIGS. 16-20 are consistentthroughout and refer to the same device components in each Figure. FIG.17 shows a cross-sectional view of the source cell 4, while FIG. 18shows a side view of the source cell 4. As seen in FIGS. 16 and 17, thesource cell 4 is in the form of a cylinder, which may be opened for thepurpose of cleaning and filling with the organic material 11. The sourcecell 4 has an inlet aperture 9 and an outlet aperture 1612. As can beseen by the arrow in FIG. 3, the flow of the carrier gas is directedthrough the inlet channel 5, the inlet aperture 9, the organic material11, the outlet aperture 12, and the outlet channel 6, the path of whichprovides for more efficient organic vapor pick-up by the carrier gas.

The preferred temperatures and pressures to be employed in the methodand with the device of the present invention are the same as thosetypically employed in organic vapor phase deposition. That is, preferredoperating pressures for the invention range from 0.01 to 10 Torr. Inaddition, preferred operating temperatures for the invention range fromabout 150° to about 500° C. This temperature range is preferred becauseat temperatures below about 150° C. the resulting vapor pressure of theorganic material is generally too low to evaporate the organic materialand transport it in the vapor phase, while at temperatures above about500° C. the decomposition of the organic material is a possible result.

In some embodiments, the one or more source cells may be heated togenerate the desired vapor pressure of the organic material within theone or more source cells. The heating of the one or more source cellscan be accomplished via a heating element and/or an insulating materialpositioned in any way such that heat reaches the one or more sourcecells. Such heating elements and insulating materials are known in theart, and are within the scope of the present invention. For example, aseparate heating element could be positioned around each individualsource cell, or a single heating element could be positioned around theentire apparatus which includes the one or more source cells. Thus, inthe embodiment of the device shown in FIG. 16, although not shown, aheating element could be placed around the source cell 4, or a heatingelement could be placed around the apparatus 2.

In addition, in some embodiments, the temperature of each of the one ormore source cells may be controlled as follows. The heating element cangenerate an axial temperature gradient along the structure which it issurrounding or adjacent to. For example, if the heating element ispositioned around the apparatus, such as the cylindrical apparatus 2shown in FIG. 16, an axial temperature gradient is generated along thecylinder, while the source cell 4 can be pulled out of or pushed intoits cylindrical source bore 8 to a desired position corresponding to thedesired temperature value. In the embodiment of the device shown in FIG.16, the range of adjustability is controlled by the temperature gradientalong the apparatus 2, the distance between the inlet and outletorifices of the source cell 4, as well as the distance and staggerbetween the carrier gas inlet channel 5 and the carrier gas outletchannel 6. In general, the rate of organic vapor delivery is controlledjointly by the source cell temperature, the flow rate of the carrier gasthrough the source cell 4, and the flow rate of the carrier gas throughthe dilution channel 10.

Embodiments of the device of the present invention are preferablycomprised of a metallic material, including but not limited to,aluminum, stainless steel, titanium, and other alloys. Preferably, thecomponents of the device of the present invention, particularly thesource cells and the apparatus in which the source bores contain thesource cells, are comprised of materials having a similar coefficient ofthermal expansion (i.e., within about 10% of one another), and morepreferably, are comprised of the same material. By employing materialsin the device with a similar coefficient of thermal expansion,differential expansion upon heating of the source cells and theapparatus in which the source bores contain the source cells is largelyavoided. Thus, upon heating the device to the desired temperature, thedevice will not encounter the potential problems of a source cellexpanding in a source bore and “locking-up” therein, or of a gapdeveloping between the source cell and the source cell allowing for theundesired passage of carrier gas therethrough. In addition, the deviceof the invention can be manufactured by methods known in the art,including but not limited to, casting, forging or machining.

In another embodiment of the invention, the one or more nozzles of thedevice are comprised of a low-emissivity material. Because the one ormore nozzles of the device are preferably within about 1 millimeter fromthe substrate, when a low-emissivity material, such as a ceramic, isused as the material for the one or more nozzles, it largely avoids theproblem of possible evaporation of previously deposited organic layerson the substrate because the low-emissivity material may emit less heatthan other materials, thereby lessening the possibility of evaporatingsuch organic layers.

In some embodiments, for example as shown in FIG. 19, the device canfurther include a selector 13 located next to the apparatus 2 which iscapable of controlling the flow of carrier gas into each carrier gasinlet channel 5. In FIG. 19, the selector 13 is placed upstream of theapparatus 2, and the selector 13 can rotate rapidly about its ownlongitudinal axis to selectively direct the flow of the carrier gas intothe inlet channels 5 and the cylindrical source bores 8. By carefullyselecting the rate at which the selector 13 rotates, the device shown inFIG. 19 can be used for the selective patterned deposition of organicvapors, for example, on a substrate.

In some embodiments, for example as shown in FIG. 20, the entireapparatus 2 is capable of rotating about its own longitudinal axis. Inthis embodiment, the flow of carrier gas into each carrier gas inletchannel 5 is controlled by the rotational position of the apparatus 2.For example, in the embodiment shown in FIG. 20, there are twostationary inlet tubes 14 placed upstream of the apparatus 2, which canrotate rapidly about its own longitudinal axis to selectively direct theflow of the carrier gas from the stationary inlet tube 14 into theselected source cell 4. By carefully selecting the rate at which theapparatus 2 rotates, the device shown in FIG. 20 can be used for theselective patterned deposition of organic vapors, for example, on asubstrate.

As the device of the invention can include one or more nozzles and oneor more source cells, embodiments of the device can include anycombination of nozzle and source cell quantities. For example, anembodiment of the device could include one nozzle and three sourcecells, wherein the three source cells include a first source cellcontaining a first organic material capable of emitting a blue spectraof light, a second source cell containing a second organic materialcapable of emitting a green spectra of light, and a third source sellcontaining a third organic material capable of emitting a red spectra oflight. Another embodiment of the device could include an array ofnozzles with one or more source cells, while still another embodiment ofthe invention could include an array of devices, each with one nozzleand a plurality of source cells. All such combinations of nozzle andsource cell quantities are within the scope of the device of the presentinvention.

In an embodiment of the method of the invention, a method of depositingan organic material is provided. The organic material may be deposited,for example, as an amorphous or crystalline film. The method comprisesmoving a substrate relative to an apparatus integrally connected to oneor more nozzles. The apparatus comprises: one or more source cells, eachsource cell containing an organic material; a carrier gas inlet leadingto each source cell; a carrier gas outlet leading from each source cellto one or more nozzles; and a first valve capable of controlling theflow of a carrier gas through the one or more source cells. The methodalso comprises controlling the composition of the organic materialand/or the rate of the organic material which is ejected by the one ormore nozzles while moving the substrate relative to the apparatus,resulting in an organic material being deposited over the substrate.

According to this embodiment of the method of the invention, the movingof a substrate relative to an apparatus can be accomplished in more thanone way. For example, the substrate can be stationary and the apparatuscan be moved in a direction parallel to the plane of the substrate. Inaddition, the apparatus can be stationary and the substrate can be movedin a direction parallel to the plane of the substrate.

Furthermore, any embodiment of the apparatus or device of the inventioncan be used in accordance with the method of the invention. For example,the embodiment of the device which includes a selector located next tothe apparatus which is capable of controlling the flow of carrier gasinto each earner gas inlet channel may be used to control thecomposition of the organic material and/or the rate of the organicmaterial which is ejected by the apparatus while moving the substraterelative to the apparatus. In addition, the embodiment of the apparatuswhich is capable of rotating about its own longitudinal axis may be usedto control the composition of the organic material and/or the rate ofthe organic material which is ejected by the apparatus while moving thesubstrate relative to the apparatus.

Embodiments of the method of the invention can be used to facilitate therapid deposition and patterning of organic materials on substrates. Forexample, the phrase “rapid deposition” may refer to the deposition of anentire display (about 3 million pixels) in about 10 seconds. Such rapiddeposition can be achieved, for example, by an embodiment of the deviceof the invention comprising a row of nozzles and a plurality of sourcecells, wherein the row of nozzles could move across a substratedepositing a different organic layer with each pass over the substrate.For example, after five passes over the substrate, a five-layered OLEDwould result. Alternatively, the same embodiment of the device couldmake just one pass over the substrate and still produce a five-layeredOLED, whereby the source cells of the device would be switched over eachpixel site such that five different layers resulted at each pixel site,provided the device had a sufficient switching time for the source cells(preferably about 10 milliseconds).

Such rapid deposition can be achieved with the device of the inventionbecause of the compactness of the device as compared to previousdevices. By positioning the organic material to be transported by thecarrier gas very close to the substrate on which it is to be depositedin accordance with the present invention, there is less latency involvedin depositing the organic layer as compared to previous configurationswith a longer distance between the organic material to be transportedand the substrate on which it is to be deposited. This longer distancebetween the organic material and the substrate which is present inprevious configurations needs to be cleared out or flushed of anyprevious organic material being transported by a carrier gas before asecond organic material can be deposited via such a configuration.However, the compactness of the device of the present invention allowsthe device to be able to rapidly deposit different organic materialswith rapid switching between the different source cells containing thedifferent organic materials. Preferably, the source cells containing theorganic materials are no greater than about 10 cm from the one or morenozzles of the device, with the one or more nozzles preferably beingwithin about 1 millimeter from the substrate.

Such rapid deposition and patterning includes both single-component anddoped organic thin films deposited on a substrate. Applications of suchpatterned organic materials on a substrate include, but are not limitedto, electronic, optoelectronic, and optical device fabrication.Furthermore, the device and method of the present invention are readilyadaptable to both large-scale deposition processes, such as thefabrication of wall-sized displays, as well as small-scale depositionprocesses, such as portable organic vapor jet printers for use inresearch laboratories and/or private homes.

The present invention will now be described in detail with respect toshowing how certain specific representative embodiments thereof can bemade, the materials, apparatus and process steps being understood asexamples that are intended to be illustrative only. In particular, theinvention is not intended to be limited to the methods, materials,conditions, process parameters, apparatus and the like specificallyrecited herein.

Experimental

Devices were fabricated using an organic vapor jet printer having anappearance similar to device 100 of FIG. 1. The organic vapor jetprinter consisted of a stainless steel, 5-source chamber, approximately40 mm in diameter and 60 mm long, with heated walls. The source cellswere 5 mm×10 mm hollow stainless steel cylinders. The source materialswere pentacene and tris(8-hydroxyquinoline)-aluminum (Alq₃), widelyemployed in organic TFT and LED work, respectively. Both materials werepre-purified twice by vacuum train sublimation and then loaded intotheir respective cells, sandwiched between two small quartz wool plugs.Depending upon the particular experiment, one or more of the five sourcecells may not have been used. Nitrogen was used as the carrier gas. Thevapor and nitrogen were forced through a collimating nozzle and onto acooled substrate, which was mounted on a computer-controlled, motorizedxyz-motion stage. The background gas pressure in the deposition chamberwas maintained between 0.1 and 1000 Torr by means of a roughing pump anda throttle valve. The deposited patterns were imaged with optical andscanning electron microscopes. The substrates used for the TFTdeposition were highly conductive silicon wafers with a 210 nm thicklayer of dry thermal SiO₂ as a gate dielectric. Prior to deposition ofpentacene, the substrates were cleaned and exposed in vacuum to asaturated vapor of octadecyl-trichlorosilane (OTS) for 15 minutes atroom temperature. The cleaning procedure consisted of sonication of theSiO₂-coated substrates in a soap solution, de-ionized water, acetone,trichloroethylene (twice), acetone (twice), and isopropanol (twice),followed by a 10-minute exposure in a UV-ozone chamber. Gold source anddrain contacts were deposited by vacuum thermal evaporation after theprinting of pentacene. A Hewlett-Packard Model 4155 parameter analyzerwas used to obtain the current-voltage transfer characteristics of theTFTs, which were tested inside of a metallic isolation box, in the dark,at ambient conditions.

FIG. 8 illustrates an image printed by OVJP at several different scales.Image 810 shows the image superimposed on a penny. Image 820 is theimage with a 1.5 mm scale line. Image 830 is the image with a 100 micronscale line. The image was generated by OVJP of Alg_(a) (flow channeldiameter α=20 μm, wall thickness L=100 μM, nozzle to substrate distances=20±10 μm, a dwell-time of 2 seconds above each pixel location, amovement time between pixels of less than 0.2 sec, upstream pressure 430Torr, downstream pressure 0.24 Torr, Alq₃ source cell temperature=270°C., substrate temperature=15° C., deposition rate approximatelyτ_(dep)=1300 Å/s). It is expected that the deposition rate could beincreased to over 8000 Å/s by increasing the source temperature to 300°C., without damaging the organic materials. At this growth rate, anarray of 800 nozzles can print an SVGA resolution display (600×800 OLEDpixels) in under one minute. This speed is comparable to the currentstate-of-the-art inkjet printers, which also use print heads containingin excess of 500 nozzles. To obtain pixels with flat-top profiles, thenozzle can be rastered or dithered laterally during growth;alternatively, a manifold of closely spaced nozzles can replace thedithered single nozzle.

FIG. 9 shows an optical micrograph of rows of pentacene dots printed onSi with a 40 μm×250 μM (α×L) nozzle outlet positioned at a distance s=30μm from the substrate. Interference fringes reflected off of thesubstrate and deposit surfaces allow the deposition shape to bedetermined, using known techniques. Each row of dots was deposited at adifferent chamber pressure (P₁=1.33, P₂=0.9, P₃=0.5, P₄=0.17 Torr),while the upstream pressure was maintained constant at Phigh=240 Torr.This combinatorial deposition shows the OVJP regime where patternresolution can be enhanced by increasing the chamber pressure. Thisresult is somewhat counterintuitive, because one might expect a higherchamber pressure to result in more scattering off of gas molecules inthe chamber (for example, as would be expected in OVPD), and thus adecreased resolution at higher chamber pressures. Instead, it has beendiscovered that a higher chamber pressure may enhance resolution.Without being limited to any theory as to how aspects of the inventionwork, it is believed that, in the flow regime of OVJP, a higher chamberpressure confines the gas jet.

Based on these results, it is expected that OVJP may be practiced athigher background pressures than one might otherwise believe. In fact,at higher pressures, there is a favorable effect on the shape of thedeposition. This favorable affect is visible at a background pressure of0.1 Torr, and becomes more pronounced at higher pressures such as 1Torr, 10 Torr and 100 Torr. As demonstrated herein, devices may befabricated at atmospheric pressure (760 Torr), which may greatly reducethe need for expensive capital equipment for fabricating devices. It isbelieved that the favorable effect may manifest at background pressuresas low as 10e-3 Torr, but may not be noticeable and as apparent asdemonstrated herein. In addition, the higher pressures (0.1 Torr andabove) may be achieved with less sophisticated vacuum apparatus, sothere is a significant advantage from a cost perspective to operating ata background pressure higher than previously thought possible.

FIG. 10 shows an optical micrograph oftris-(8-hydroxyquinoline)-aluminum (Alq₃) dots printed onto Si using a20 μm×100 μm nozzle, at P_(high)=240 Torr and P_(low)=0.24 Torr. Thedistance from the nozzle outlet to the substrate s was varied (25, 53.4,81.8, 110.2, 138.2, and 167)±10 microns, with S1=25 and S6=167 μm. Thedwell time at each dot location was 60 seconds.

FIG. 11 shows thickness profiles calculated from the interference fringepatterns of FIG. 10. For sufficiently thick deposits, light-interferencefringes allow the deposit profile to be determined.

Equation (8) predicts that the pattern dispersion, χ, should scale ass^(1/2). FIG. 12 shows that (FWHM)² scales linearly with s, in agreementwith Eq. (8). The full width-half maximum (FWHM), as taken from thethickness profiles of FIG. 11 after normalization, was used as a measureof χ.

FIG. 13 shows a scanning electron micrograph (SEM) of a pentacene lineprinted on SiO₂ with a local deposition rate >300 Å/s and s=35±15 μm.Image 1310 is the pentacene line with a 500 micron scale line, whileimages 1320 are the same pentacene line at a higher magnification with a1 micron scale line. The image reveals that the pentacene grows in theshape of slanted nano-pillars. The nano-pillars situated to the left andthe right of the jet center tilt in toward the nozzle, toward thedirection from which gas flows. This effect is not observed indiffusion-limited growth, such as occurs in OVPD, but may be caused bythe self-shadowing of pentacene crystallites during the highlydirectional “feed” of the crystals during the OVJP process. Thisdirectionality is due to the anisotropic molecular velocity distributionin the gaseous jet. A similar crystal growth mode has been observedduring glancing angle deposition of metals. Seeding the organicmolecules in a fast-flowing carrier stream also allows near-tohyper-thermal velocities to be reached by the adsorbent and,consequently, the tuning of incident kinetic energy. This decouples thefilm crystallization dynamics from surface temperature, leading tohighly ordered films even for relatively cold substrates. This effecthas important implications for improving the performance of devices,such as polycrystalline channel TFTs.

To demonstrate the feasibility of the very high local deposition ratesfor device application, OVJP was used to print pentacene channel TFTs.The pentacene channel was printed in the form of a 6 mm×6 mm uniformlyfilled square by rastering the narrow jet over a 5 mm×5 mm substratearea. The TFT channels were defined by the Au drain-source electrodes,which were deposited in vacuum immediately following the printing ofpentacene. The printing employed a 350 μm diameter nozzle, with s=1000μm, T_(source)=220° C., T_(substrate)=20° C., Q_(source)=5 sccm,Q_(dilution)=5 sccm, P_(high)=20 Torr, and P_(low),=0.165 Torr,resulting in a local pentacene growth rate ˜700 Å/s.

The active pentacene channel had a gate width/length ratio of 1000/45(±5) μm, and consisted of a 5000 Å thick pentacene film with an averagegrain diameter of <200 nm. The device drain-source current (I_(DS))versus voltage (V_(DS)) characteristic is plotted in FIG. 14, showingthe drain-source current saturation behavior similar to that previouslyobserved for vacuum and OVPD grown pentacene TFTs. The characteristicwas obtained from the drain-source current saturation regime atV_(DS)=−40V. The TFT exhibited some hysteresis in the I_(DS vs)-V_(GS)behavior, with the threshold voltage shifting from +10 to +17 V in theforward and reverse V_(GS) directions, as indicated. The I_(DS) vs. thegate bias (V_(GS)) is plotted in FIG. 15, revealing an I_(DS) on/offratio of 7·10⁵ and a channel field-effect hole mobility ofμ_(eff)=0.25±0.05 cm²/V·s in the saturation regime. The hole mobility ofa vacuum-deposited control TFT deposited via thermal evaporation wassimilar, but, due to thinner pentacene in the channel region, it showeda smaller source-drain off current.

Organic vapor jet printing was also used to print pentacene TFTs innitrogen at atmospheric pressure; the TFTs exhibited=0.2 cm²/V·s. Thehole mobility of a vacuum-deposited control TFT was within theexperimental error of the values obtained by OVJP at P_(L) 0.2 Torr. Thecost of device and circuit fabrication can be significantly reduced bythe ability to directly print small-molecular organic transistors atambient conditions, such as in a nitrogen glove box.

The deposition of a working device at atmospheric pressure isparticularly significant, because it demonstrates the feasibility ofusing OVJP without expensive and cumbersome vacuum equipment thatrequires time to pump down. For example, the ability to deposit atatmospheric pressure may greatly facilitate the deposition of organicmaterials in a large scale assembly line. It may be desirable to depositin a controlled atmosphere to avoid impurities, such as in a glove boxfilled with an inert gas such as nitrogen, but such a controlledatmosphere may be significantly cheaper, easier and faster to provide ascompared to a vacuum. Another way to control impurities from an ambientatmosphere is to use a guard flow, such as that produced by the deviceillustrated in FIG. 2.

EXAMPLES Example 1

In Example 1, an embodiment of the device of the invention as seen inFIG. 16 was used to deposit an organic material on a silicon substrate.That is, the device included a single source cell 4 containing anorganic material, aluminum tris(8-hydroxyquinoline) (Alq₃), and a singlenozzle 1 with an inner diameter of about 350 μm. In this example, thedistance between the end of the nozzle 1 and the substrate was in therange of about 0.5 to about 1.0 mm, the deposition pressure was about270 mTorr, and the source cell temperature was about 222° C.

FIG. 21 shows a photograph of the deposited Alq₃ from Example 1 (from anoverhead view looking down on the deposited Alq₃) showing interferencefringes due to the variation in thickness of the deposited Alq₃. Thewidth of the deposited Alq₃ shown in FIG. 21 is approximately 500 μm.

Example 2

In Example 2, an embodiment of the device of the invention as seen inFIG. 16 was used to deposit an organic material on a silicon substrate.That is, the device included a single source cell 4 containing anorganic material, Alq₃, and a single nozzle 1. However, in theembodiment of the device used in Example 2, the nozzle 1 had an innerdiameter of approximately 50 μm. In this example, the distance betweenthe end of the nozzle 1 and the substrate was in the range of about 0.5to about 1.0 mm, the deposition pressure was about 270 mTorr, and thesource cell temperature was varied within the range of 209° to 225° C.

FIG. 22 shows a photograph of the deposited Alq₃ from Example 2 (from anoverhead view looking down on the deposited Alq₃) showing interferencefringes due to the variation in thickness of the deposited Alq₃. Thewidth of the deposited Alq₃ shown in FIG. 22 is approximately 100 μm.

The physical shape of the deposited Alq₃ from Example 2 is shown in FIG.23. Curve 81 represents the light intensity profile of the photograph ofthe deposited Alq₃ from Example 2 (which is shown in FIG. 22), graphedas arbitrary units of intensity as a function of x (μm), wherein xrepresents the distance from the center (0) of the deposited Alq₃. Thelight intensity profile 81 was then translated into curve 82 whichrepresents the physical shape of the deposited Alq₃ from Example 2,plotted as thickness (rim) as a function of x (μm). As can be seen inFIG. 23, curve 82 approximates a bell-shaped curve, wherein duringdeposition the center of the nozzle 1 is located approximately over thecenter of the deposited organic material, denoted on the x-axis of FIG.23 by the numeral “0.” Thus, in order to flatten-out this bell-shapedcurve and deposit an organic material with a flatter profile, the nozzlecould be dithered over a desired distance during the deposition processthereby producing a flatter deposited organic material than that shownin FIG. 23. Furthermore, a device of the invention could include morethan one nozzle 1 arranged in a linear array with proper spacing betweenthe nozzles such that the hell-shaped deposits from each nozzle 1 wouldoverlap to the extent that the profile of the resulting organic materialdeposited from the array of nozzles would more closely approximate aplateau rather than a bell-shaped curve.

Example 3

In Example 3, an embodiment of the device of the invention as seen inFIG. 16 was used to deposit an organic material as part of thefabrication of an OLED. The structure of the fabricated OLED 98 can beseen in FIG. 24.

The process used to fabricate the OLED 98 shown in FIG. 24 proceeded asfollows. A substrate 91 was comprised of a 12.5 mm×12.5 mm×1 mm glassslide. The substrate 91 was pre-coated with a layer 92 of indium tinoxide (ITO), which served as the anode of the OLED 98 structure. A holeinjection layer 93 was deposited onto the ITO-layer 92, wherein the holeinjection layer 93 comprised about 100 Å of copper phthalocyanine(CuPc). A hole transporting layer 94 was deposited onto the holeinjection layer 93, wherein the hole transporting layer 94 comprisedabout 450 Å of 4,4′-bis[N-(1-napthyl)-N-phenyl-amino]biphenyl (α-NPD).

Next, an embodiment of the device of the invention as seen in FIG. 16was used to deposit dots 95 of the organic material Alq₃, a greenemitter, onto the hole transporting layer 94, but only on one half ofthe hole transporting layer 94 as shown in FIG. 24. The deposited dots95 were each approximately 150 Å thick. The device used to deposit thedots 95 included a single source cell 4 containing the Alg_(a), and asingle nozzle 1 having a length of about 5 mm and an inner diameter ofabout 50 μm. While depositing the dots 95, the distance between the endof the nozzle 1 and the hole transporting layer 94 was about 200 μm, thedeposition pressure was about 275 mTorr, the source cell temperature wasabout 220° C., and the deposition rate was about 1.25 Å/sec.

An electron transporting layer 96 was then deposited over the dots 95,and over the portions of the hole transporting layer 94 which were notcovered by the dots 95. The electron transporting layer 96 comprisedabout 500 Å of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP).Next, cathodes 97 were deposited over the electron transporting layer96, one over the half of the OLED 98 containing the dots 95, and oneover the other half of the OLED 98. The cathodes 97 each comprised anabout 7 Å-thick layer of LiF, capped by an about 1500 Å-thick layer ofAl. The depositions of all of the layers of the OLED 98 of Example 3,except for the deposition of the dots 95 as discussed above, were donevia high vacuum (˜10⁻⁶ Torr) thermal evaporation.

FIG. 25 shows a depiction of the electroluminescent (EL) intensity as afunction of wavelength for the OLED 98 fabricated in Example 3. Thethree different curves shown in FIG. 25 denote different portions of theOLED 98; namely, curve 101 represents that portion of the OLED 98containing the dots 95, while curves 102 and 103 represent two differentlocations within that portion of the OLED 98 not containing the dots 95.Thus, the only OLED structural difference represented by these curves101, 102 and 103 is that curve 101 includes Alq₃ dots 95 deposited by anembodiment of the device of the invention as described above. As can beseen in FIG. 25, although all three curves 101, 102 and 103 display apeak EL intensity at about 445 nm, only curve 101 has an additional peakintensity at about 520 nm. This additional peak at about 520 nm shown incurve 101 can be attributed to the green emission of the Alq₃ dots 95which were deposited by the embodiment of the device of the invention asdescribed above.

Although the present invention is described with respect to particularexamples and preferred embodiments, it is understood that the presentinvention is not limited to these examples and embodiments. The presentinvention as claimed therefore includes variations from the particularexamples and preferred embodiments described herein, as will be apparentto one of skill in the art.

What is claimed is:
 1. A method of depositing an organic material,comprising: ejecting a carrier gas carrying an organic material from anozzle at a flow velocity that is at least 10% of the thermal velocityof the carrier gas, to form a layer of organic material on a substrate,the layer comprising a plurality of separate films; wherein a dynamicpressure in a region between the nozzle and the substrate surroundingthe carrier gas is at least 1 Torr.
 2. The method of claim 1, whereinthe dynamic pressure is at least 10 Torr.
 3. The method of claim 2,wherein the background atmosphere is at least 5 Torr.
 4. The method ofclaim 2, further comprising: providing a guard flow surrounding theorganic material ejected from the nozzle.
 5. The method of claim 4,wherein the background atmosphere is ambient atmosphere at about 760Torr.
 6. The method of claim 2, wherein the dynamic pressure of at least10 Torr is affected by a guard flow ejected from the nozzle.
 7. Themethod of claim 6, wherein the background pressure is the base pressureof a vacuum chamber, and is less than about 0.1 Torr.
 8. The method ofclaim 7, wherein the molecular weight of the organic material is greaterthan the molecular weight of the carrier gas.
 9. The method of claim 6,wherein the guard flow comprises a first gas, the carrier gas comprisesa second gas, and the molecular weight of the first gas is greater thanthe molecular weight of the second gas.
 10. The method of claim 1,wherein the dynamic pressure is at least about 760 Torr.
 11. The methodof claim 1, wherein the dynamic pressure is not greater than about 2times the background pressure.
 12. The method of claim 1, wherein thedynamic pressure is not greater than about 10 times the backgroundpressure.
 13. The method of claim 1, wherein the plurality of separatefilms comprises a plurality of pixels.
 14. The method of claim 1,wherein at least one of the nozzle diameter, the nozzle length, and thenozzle-to-substrate separation is about equal to the gas mean free pathlength.
 15. The method of claim 1, wherein the dynamic pressure is atleast 0.5 Torr greater than the background pressure.